1# SPDX-License-Identifier: GPL-2.0-only 2# 3# Timer subsystem related configuration options 4# 5 6# Options selectable by arch Kconfig 7 8# Watchdog function for clocksources to detect instabilities 9config CLOCKSOURCE_WATCHDOG 10 bool 11 12# Architecture has extra clocksource init called from registration 13config ARCH_CLOCKSOURCE_INIT 14 bool 15 16# Timekeeping vsyscall support 17config GENERIC_TIME_VSYSCALL 18 bool 19 20# The generic clock events infrastructure 21config GENERIC_CLOCKEVENTS 22 def_bool !LEGACY_TIMER_TICK 23 24# Architecture can handle broadcast in a driver-agnostic way 25config ARCH_HAS_TICK_BROADCAST 26 bool 27 28# Clockevents broadcasting infrastructure 29config GENERIC_CLOCKEVENTS_BROADCAST 30 bool 31 depends on GENERIC_CLOCKEVENTS 32 33# Handle broadcast in default_idle_call() 34config GENERIC_CLOCKEVENTS_BROADCAST_IDLE 35 bool 36 depends on GENERIC_CLOCKEVENTS_BROADCAST 37 38# Automatically adjust the min. reprogramming time for 39# clock event device 40config GENERIC_CLOCKEVENTS_MIN_ADJUST 41 bool 42 43# Generic update of CMOS clock 44config GENERIC_CMOS_UPDATE 45 bool 46 47# Select to handle posix CPU timers from task_work 48# and not from the timer interrupt context 49config HAVE_POSIX_CPU_TIMERS_TASK_WORK 50 bool 51 52config POSIX_CPU_TIMERS_TASK_WORK 53 bool 54 default y if POSIX_TIMERS && HAVE_POSIX_CPU_TIMERS_TASK_WORK 55 56config LEGACY_TIMER_TICK 57 bool 58 help 59 The legacy timer tick helper is used by platforms that 60 lack support for the generic clockevent framework. 61 New platforms should use generic clockevents instead. 62 63config TIME_KUNIT_TEST 64 tristate "KUnit test for kernel/time functions" if !KUNIT_ALL_TESTS 65 depends on KUNIT 66 default KUNIT_ALL_TESTS 67 help 68 Enable this option to test RTC library functions. 69 70 If unsure, say N. 71 72config CONTEXT_TRACKING 73 bool 74 75config CONTEXT_TRACKING_IDLE 76 bool 77 select CONTEXT_TRACKING 78 help 79 Tracks idle state on behalf of RCU. 80 81menu "Timers subsystem" 82 83if GENERIC_CLOCKEVENTS 84# Core internal switch. Selected by NO_HZ_COMMON / HIGH_RES_TIMERS. This is 85# only related to the tick functionality. Oneshot clockevent devices 86# are supported independent of this. 87config TICK_ONESHOT 88 bool 89 90config NO_HZ_COMMON 91 bool 92 select TICK_ONESHOT 93 94choice 95 prompt "Timer tick handling" 96 default NO_HZ_IDLE if NO_HZ 97 98config HZ_PERIODIC 99 bool "Periodic timer ticks (constant rate, no dynticks)" 100 help 101 This option keeps the tick running periodically at a constant 102 rate, even when the CPU doesn't need it. 103 104config NO_HZ_IDLE 105 bool "Idle dynticks system (tickless idle)" 106 select NO_HZ_COMMON 107 help 108 This option enables a tickless idle system: timer interrupts 109 will only trigger on an as-needed basis when the system is idle. 110 This is usually interesting for energy saving. 111 112 Most of the time you want to say Y here. 113 114config NO_HZ_FULL 115 bool "Full dynticks system (tickless)" 116 # NO_HZ_COMMON dependency 117 # We need at least one periodic CPU for timekeeping 118 depends on SMP 119 depends on HAVE_CONTEXT_TRACKING_USER 120 # VIRT_CPU_ACCOUNTING_GEN dependency 121 depends on HAVE_VIRT_CPU_ACCOUNTING_GEN 122 select NO_HZ_COMMON 123 select RCU_NOCB_CPU 124 select VIRT_CPU_ACCOUNTING_GEN 125 select IRQ_WORK 126 select CPU_ISOLATION 127 help 128 Adaptively try to shutdown the tick whenever possible, even when 129 the CPU is running tasks. Typically this requires running a single 130 task on the CPU. Chances for running tickless are maximized when 131 the task mostly runs in userspace and has few kernel activity. 132 133 You need to fill up the nohz_full boot parameter with the 134 desired range of dynticks CPUs to use it. This is implemented at 135 the expense of some overhead in user <-> kernel transitions: 136 syscalls, exceptions and interrupts. 137 138 By default, without passing the nohz_full parameter, this behaves just 139 like NO_HZ_IDLE. 140 141 If you're a distro say Y. 142 143endchoice 144 145config CONTEXT_TRACKING_USER 146 bool 147 depends on HAVE_CONTEXT_TRACKING_USER 148 select CONTEXT_TRACKING 149 help 150 Track transitions between kernel and user on behalf of RCU and 151 tickless cputime accounting. The former case relies on context 152 tracking to enter/exit RCU extended quiescent states. 153 154config CONTEXT_TRACKING_USER_FORCE 155 bool "Force user context tracking" 156 depends on CONTEXT_TRACKING_USER 157 default y if !NO_HZ_FULL 158 help 159 The major pre-requirement for full dynticks to work is to 160 support the user context tracking subsystem. But there are also 161 other dependencies to provide in order to make the full 162 dynticks working. 163 164 This option stands for testing when an arch implements the 165 user context tracking backend but doesn't yet fulfill all the 166 requirements to make the full dynticks feature working. 167 Without the full dynticks, there is no way to test the support 168 for user context tracking and the subsystems that rely on it: RCU 169 userspace extended quiescent state and tickless cputime 170 accounting. This option copes with the absence of the full 171 dynticks subsystem by forcing the user context tracking on all 172 CPUs in the system. 173 174 Say Y only if you're working on the development of an 175 architecture backend for the user context tracking. 176 177 Say N otherwise, this option brings an overhead that you 178 don't want in production. 179 180config NO_HZ 181 bool "Old Idle dynticks config" 182 help 183 This is the old config entry that enables dynticks idle. 184 We keep it around for a little while to enforce backward 185 compatibility with older config files. 186 187config HIGH_RES_TIMERS 188 bool "High Resolution Timer Support" 189 select TICK_ONESHOT 190 help 191 This option enables high resolution timer support. If your 192 hardware is not capable then this option only increases 193 the size of the kernel image. 194 195config CLOCKSOURCE_WATCHDOG_MAX_SKEW_US 196 int "Clocksource watchdog maximum allowable skew (in microseconds)" 197 depends on CLOCKSOURCE_WATCHDOG 198 range 50 1000 199 default 125 200 help 201 Specify the maximum amount of allowable watchdog skew in 202 microseconds before reporting the clocksource to be unstable. 203 The default is based on a half-second clocksource watchdog 204 interval and NTP's maximum frequency drift of 500 parts 205 per million. If the clocksource is good enough for NTP, 206 it is good enough for the clocksource watchdog! 207endif 208 209config POSIX_AUX_CLOCKS 210 bool "Enable auxiliary POSIX clocks" 211 depends on POSIX_TIMERS 212 help 213 Auxiliary POSIX clocks are clocks which can be steered 214 independently of the core timekeeper, which controls the 215 MONOTONIC, REALTIME, BOOTTIME and TAI clocks. They are useful to 216 provide e.g. lockless time accessors to independent PTP clocks 217 and other clock domains, which are not correlated to the TAI/NTP 218 notion of time. 219 220endmenu 221